Speed

[Weta43]

That's what I mean though - my old man was 6'6" & weighed 18 stone - what does that mean to my 12 year old? - nothing, but 2m tall & 115kg is much more understandable.

[EtherealN]

Very true. :)

 

Though it should be said that as far as I know the Celcius temperature scale is not directly linked to the metric system, and it actually has some rather nasty inconsistencies. It is very practical in having the 0 to 100 scale placed in places that make a lot of sense to our everyday lives, but it is very dependant on conditions. On the top of Mt. Everest water boils at ~92 degrees C (rough from memory, don't quote me), and there are underwater vents where some really awesome microbes live happily in water that is several hundred degrees hot - but due to the pressure it is still water and it's not boiling.

[hitman]

Well, all metrics are based off of a universal measurement. For example:

Sea level at 60 degrees on a sunny day, 29.92" Hg.

14.7 millibars at same altitude and atmospheric pressure (1 psi)

Absolute Humidity

Degrees Calvin, Rankin (absolute temp molecules stop moving)

 

Id like to know if anyone takes physics into account when it comes to absolute in different atmospheres, Like does water boil at 100c at Mt Everests peak and still freeze at 0c...Pascals law, Charles laws, and Boyles laws cant be ignored.

[EtherealN]

I'm not entirely certain, but my understanding of how they do it was that originally (in the case of C) it was quite simply just defined as "freezing=0 and boiling=100", but as scientists noticed that actual thermal energy on those points will differ depending on environment and that the definition of those points today end up being sort of pegged to the Kelvin scale which is easier for those things because it's not based on things that depend on environment. (AFAIK.)

 

So today Celcius is based on three things to establish the scale - 0 Kelvin (it's "incorrect" to say "0 degrees Kelvin", it's just "0 Kelvin") is −273.15 °C, and the 0 and 100 points is then defined with specific athmospheric conditions in mind.

 

So today, no, water does not boil at 100C on Mt Everest, and the scales compensate.

 

One can compare to how the definition of a meter was changed to adjust for variable environments - originally there were the "standard meter" rods in Paris (I think it was), and they as physical objects served as the standard. But then it was realized that even they will vary in size depending on temperature, so there was a switch to a system based on the size of the earth. (I think it was the circumference of the earth divided a specific amount of times.) But the earth is also variable so sometime in like the 80's the international standard changed to be a certain distance covered in a specific amount of time in a vacuum - apparently that also fixes a lot of issues with distance measurements at relativistic regimes.

 

But afaik they've not made the definition adjustable for quantum vacuums so it might be found to be too inexact again at some point. >.<

 

So as far as I've checked (and obviously I haven't checked every unit out there) it would seem like the standards have progressively been changed to take physics of all sorts into account as they are discovered, which ends up in there being differences between what a unit meant at different points in time.

[Weta43]

You're right - at least not in the same way Kilograms, meters, seconds are used to derive >> newtons, joules, watts etc, but degrees Celcius and Degrees Kelvin are the same "size" just have different starting points. Moving from one to the other you just need to add or subtract a constant.

 

You're right again - Water doesn't always boil at 100 or freeze at zero - that's true, but for pure water at 1 atmosphere pressure it's near enough for most practical purposes - and to the extent it's not true, it doesn't boil at 212 & freeze at 32 farenheit either :-)

 

 

Amazing - You've already written an expanded version of my reply to your post !!!

Edited April 19, 2009 by Weta43

[EtherealN]

Aye, I actually checked the differences and pure water at one atmosphere freeses on like 0.01°C and boils at 99.9839°C.

 

The difference between those and 0 and 100 is... not really all that important in everyday life. :P Just like even the old meter rods back in Paris were and still are perfectly good for most of us even if one completely disregards environment. The hell do I care if my yardstick has an error of a thousandth of a millimeter? So for most of us it's all academic, but it is pretty interesting to delve into the subject of how exact scientists have to get things as they work on whatever they're working on.

[EtherealN]

Amazing - You've already written an expanded version of my reply to your post !!!

 

Hahah, I'm psychic! Really! Give me money and I'll tell you what your next post is gonna be! :D

[slug88]

I'm not entirely certain, but my understanding of how they do it was that originally (in the case of C) it was quite simply just defined as "freezing=0 and boiling=100", but as scientists noticed that actual thermal energy on those points will differ depending on environment and that the definition of those points today end up being sort of pegged to the Kelvin scale which is easier for those things because it's not based on things that depend on environment. (AFAIK.)

 

This is wrong. The Kelvin scale depends just as much on environment as does the Celsius scale. In fact the scales are identical, save for a shift of ~273 degrees between a measurement in kelvin and a measurement in Celsius. (Tk = Tc + 273)

 

Also, I'm pretty certain that it was known that water boiled and froze at different temperatures which depended upon atmospheric conditions when the Celsius scale was drafted. The fact that water doesn't always boil at 100C is not an "inconsistency", as the Celsius scale is a measure of temperature, not of the boiling point of water. Obviously the boiling of water is not solely correlated to temperature, and so any temperature scale will give different boiling points for water.

 

Edit: Looks like my reply's a little late to the party. When did this forum get so fast paced!

Edited April 19, 2009 by slug88

[EtherealN]

Well, I'm not really sure I agree. They are identical because the Celcius scale got pegged to Kelvin. I am really not sure what you mean by Kelvin depending on environment though - it's an absolute scale that measures the underlying property that causes the temperature phenomenon.

 

So in that sense they're both absolute now.

 

What environmental variable would make Kelvin read differently in two environmental states where the thermal energy is equal? (EDIT: I tried to look up the maths of it but it got way beyond my own math skills. >.< )

Edited April 19, 2009 by EtherealN

[hitman]

This is wrong. The Kelvin scale depends just as much on environment as does the Celsius scale. In fact the scales are identical, save for a shift of ~273 degrees between a measurement in kelvin and a measurement in Celsius. (Tk = Tc + 273)

Kelvin is for Celsius and Rankin is for Fahrenheit, correct?

 

Well, I'm not really sure I agree. They are identical because the Celcius scale got pegged to Kelvin. I am really not sure what you mean by Kelvin depending on environment though - it's an absolute scale that measures the underlying property that causes the temperature phenomenon.

 

So in that sense they're both absolute now.

 

What environmental variable would make Kelvin read differently in two environmental states where the thermal energy is equal?

I would assume the difference between density of the material and atmospheric pressure. Obviously a vacuum will try to pull the molecules apart, which would create friction. Would it?

Edited April 19, 2009 by hitman

[EtherealN]

Well, that depends on what you mean by a vacuum. Mass Vacuum or Energy Vacuum? This is where the maths destroyed me, since we (as in, laymen like me) usually thinks of temperature as something that matter has, but even a volume of space that has no matter in it will still not be at 0K.

 

EDIT: On your latter example, the friction, my understanding (I can be wrong and if someone can correct it I'll ♥ you) is that the friction would cause an increase in thermal energy and therefore the temperature in K would increase.

Edited April 19, 2009 by EtherealN

[hitman]

A mass vacuum. Dead empty space that has no matter can retain heat in the form of radiation, and thats theoretically the only way possible. However, something has to absorb that thermal energy. So if dead empty space has no electrons, protons or neutrons, there isnt any heat conduction.....

 

 

 

This has nothing to do with metrics!

 

 

 

 

 

:mad:

[EtherealN]

True enough. :P

 

And yeah, we probably should give it a chance to return to the topic. As a final note of trivia I'll link you all to an article on the machine that has created the highest man-made temperatures ever - the Z-machine! http://en.wikipedia.org/wiki/Z_machine

 

2.66 to 3.7 BILLION Kelvin. I want one! :D

[Coolhnd1]

You have to laugh at how a thread that started out asking how you can make the Ka-50 go a certain speed ends being a technical discussion on the metric system because of a joke that was initially taken the wrong way.

[EtherealN]

That is very true. :)

[hitman]

Very true. :), and there are underwater vents where some really awesome microbes live happily in water that is several hundred degrees hot - but due to the pressure it is still water and it's not boiling.

I just remembered this...those arent water jets your talking about, those are steam vents. They arent boiling, its already steam. Now Ill get on my high horse and ride my ass outta here.

[EtherealN]

I know, what I'm talking about is the water AROUND the vent streams (like the black smokers etc) themselves.

 

But I can be wrong on that count, it's one of those things you pick up and only barely remember anything resembling specifics of.

 

We so should get the thread split and then have a dedicated thread to this. :P